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Mammalian Elastic Cartilage

Connective tissue includes bone, cartilage, tendons, and fatty tissues. Differing from articular (or hyaline) cartilage that depends on a stiff, fibrillar collagen network with fluid-filled spaces, mammalian elastic cartilage contains little or no collagen. Rather, elastic cartilage relies on other fibrillar matrix proteins for structural integrity. Elastin, the most well-studied of these proteins, forms the matrix of elastic cartilages typical of the mammalian ear, laryngeal tissues, and the epiglottis.

As one of the standard histology preparations for microscopy, mammalian elastic cartilage is often taken from laboratory rats or rabbits. Using polarizing light microscopy, the microscopist can quantitatively investigate the optical properties of isolated elastin fibers. The elastin fibers are a characteristic yellow in color and extend through the cartilage matrix in all directions. Mammalian elastic cartilage maintains the shape and flexibility of structures or organs such as the rabbit ear, while supporting and strengthening them.

As cartilage grows, mitosis takes place, but because of the matrix, the daughter cells cannot migrate. Thus, cartilage cells, or chondrocytes, tend to occur in small clusters, with each cluster representing a group of cells produced by many cellular divisions in the immediate region. Chondrocytes bear a close resemblance to fibroblasts, and in the formation of new cartilage, fibroblasts can differentiate into chondroblasts, form new cartilage, and then transform into chondrocytes, which are the maintenance cells of established cartilage tissue.